Datasheet

CY8C21x34/B CapSense
®
Design Guide Document No. 001-66271 Rev. *B 21
3.6 CSD User Module High-Level Parameters
3.6.1 Finger Threshold
The Finger Threshold parameter is used by the user module to judge the active/inactive state of a sensor. If the
Difference Count value of a sensor is greater than the Finger Threshold value, the sensor is judged as active. This
definition assumes that Hysteresis is set to zero and Debounce is set to 1.
Possible values are 5 to 255.
3.6.2 Noise Threshold
The user module uses the Noise Threshold value to interpret the upper limit of noise counts in the raw count. For
individual sensors, the baselining update algorithm is paused when the raw count is greater than the baseline and the
difference between them is greater than this threshold.
For slider sensors, the centroid calculation is paused when the difference count is greater than the Noise Threshold
value.
Possible values are 3 to 255. For proper user module operation, the Noise Threshold value should never be set
higher than Finger Threshold value minus the Hysteresis setting.
3.6.3 Baseline Update Threshold
When the raw count value is above the current baseline and the difference count is below the noise Threshold, the
difference between the current baseline and the raw count is accumulated into a "bucket." When the bucket fills
completely, the baseline increments and the bucket is emptied. The Baseline Update Threshold parameter sets the
threshold that the bucket must reach for the baseline to increment.
Possible values are 0 to 255.
3.6.4 Sensors Autoreset
The Sensors Autoreset parameter determines whether the baseline is updated at all times, or only when the
difference counts are less than the Noise Threshold value.
When Sensors Autoreset is enabled, the baseline is updated constantly. This limits the maximum time duration of the
sensor but prevents the sensors from permanently turning on when the raw count accidentally rises without anything
touching the sensor. This sudden rise can be caused by a large voltage fluctuation in the power supply, a high-energy
RF noise source, or a very quick temperature change.
When Sensors Autoreset is disabled, the baseline is updated only when the difference counts are less than the Noise
Threshold parameter.
Possible values are Enabled and Disabled.
3.6.5 Hysteresis
The Hysteresis setting prevents the sensor ON state from chattering because to system noise. The function of
Hysteresis is given in Equation 4. The equation assumes that Debounce is set to 1.